1. Field of the Invention
The present invention relates to a network address converting apparatus and a computer readable medium on which a network address conversion program is stored, whereby it becomes possible to provide push-type information service via the Internet to a client which is located within a local network and which has no Internet IP address.
2. Description of the Related Art
In general, a client connected to, for example, a local area network (LAN) is assigned an IP address defined in that LAN (hereinafter referred to as a local IP address). When this client communicates with a host server connected to, for example, the Internet (hereinafter referred to as an external host), it is required that the client use an Internet IP address assigned to the client in which Internet IP addresses are managed by Internet society.
When a client located within a LAN and having no Internet IP address gets access to an external host, the client requests, for example, a router having a network address translation (NAT) capability to assign an Internet IP address. The router selects one of the Internet IP addresses registered in advance and assigns the selected Internet IP address to the client.
In the case where data is transmitted from the client to the external host, the router having the NAT capability converts the local IP address of the client to the Internet IP address assigned to that client. On the other hand, when data addressed to the client is received from the external host, the router converts the IP address designating the destination (that is the Internet IP address assigned to the client) to the local address of the client. Thus, communication between the client within the LAN and the external host is achieved.
In recent years, push-type information service is provided in which information is sent from an external host to a particular client even when the client does not issue a request. However, the conventional technique does not allow clients within a LAN to receive pushtype information service.
This is because, for example, the router having the NAT capability can assign an Internet IP address to a client only when assignment is requested by the client and cannot assign an Internet IP address to a client within the LAN in response to an access request from an external host.
In view of the above, it is an object of the present invention to provide a network address converting apparatus and a computer readable storage medium on which a network address conversion program is stored, whereby an external host can provide push-type information service even to a client within a local network via the Internet.
It is another object of the present invention to provide a network address converting apparatus and a computer readable storage medium on which a network address conversion program is stored, whereby an external host can provide push-type information service to a client within a radio communication network including a plurality of subnetworks each including a server and a client connected to each other via radio communication wherein the client is movable among the plurality of subnetworks.
To achieve these and other objects, the present invention provides a network address converting apparatus for converting a source address or a destination address included in data transmitted between an external host server connected to the Internet and a client within a local network. The network address converting apparatus when an assignment request signal requesting assignment of an Internet IP address to a particular client within the local network is received from the external host server, the network address converting apparatus assigns an Internet IP address to the particular client and notifies the external host server of the assigned Internet IP address; and when data addressed to the assigned Internet IP address is received from the external host server, the network address converting apparatus converts the destination of the received data to the particular client""s address defined in the local network.
The network address converting apparatus preferably includes: data analyzing means which receives data transmitted between the external host server and a client and analyzes the type, the destination, and the sender of the data; IP address assigning means which, if the data analyzing means determines that the received data is an Internet IP address assignment request signal sent from the external host server, selects one of a plurality of Internet IP addresses stored in advance in the IP address assigning means and assigns the selected Internet IP address to the client which is requested to be assigned an Internet IP address by the Internet IP address assignment request signal; address conversion table producing means which, each time said IP address assigning means assigns an Internet IP address to a client, stores in a relational fashion the Internet IP address assigned to said client and the client""s address defined in said local network thereby producing an address conversion table; address conversion means which, each time the IP address assigning means assigns an Internet IP address to a client, sends the assigned Internet IP address to the sender of the Internet XP address assignment request signal, and which, if the data analyzing means determines that the received data is addressed to the Internet IP address assigned to the client, converts the Internet IP address designating the destination of the data to the corresponding address defined in the local network by referring to the address conversion table.
According to another aspect of the invention, there is provided a network address converting apparatus for converting a source address or a destination address included in data transmitted between an external host server connected to the Internet and a mobile terminal within a radio communication network system, the radio communication network system including a plurality of subnetworks each including at least one mobile terminal and at least one wireless server connected via radio communication to the at least one mobile terminal, the mobile terminal being movable among the plurality of subnetworks, each wireless server storing and managing the Internet IP address of a wireless server which controls a subnetwork in which one or more mobile terminals, for which the wireless server serves as the home server, are currently located, said network address converting apparatus being characterized in that: the network address converting apparatus is provided for each wireless server; and the network address converting apparatus operates in such a manner that: when an inquiry signal about the current location of a particular mobile terminal is sent from an external host server to a home server of the particular mobile terminal, if the network address converting apparatus receives the inquiry signal, it notifies the external host server of the Internet IP address of the wireless server which controls a subnetwork in which the particular mobile terminals is currently located; when an assignment request signal requesting assignment of an Internet IP address to the particular mobile terminal is received from the external host server, the network address converting apparatus assigns an Internet IP address to the particular mobile terminal and notifies the external host server of the assigned Internet IP address; and when data addressed to the assigned Internet IP address is received from the external host server, the network address converting apparatus converts the destination of the received data to the particular mobile terminals address defined in the subnetwork in which the particular mobile terminal is currently located.
Preferably, the network address converting apparatus includes: data analyzing means which receives data transmitted between the mobile terminal and the external host server connected to the Internet and analyzes the type, the destination, and the sender of the data; current location retrieving and notifying means which, if the data analyzing means determines that the received data is an inquiry signal about the current location of a particular mobile terminal sent from the external host server, searches the mobile terminals stored in the respective wireless servers and the Internet IP addresses of wireless servers controlling subnetworks in which the respective terminals are currently located so as to detect the Internet IP address of the wireless server which controls the subnetwork in which the particular mobile terminal is currently located, and sends the detected Internet IP address to the sender of the inquiry signal; IP address assigning means which, if the data analyzing means determines that the received data is an Internet IP address assignment request signal sent from the external host server, selects one of a plurality of Internet IP addresses stored in advance in the IP address assigning means and assigns the selected Internet IP address to the mobile terminal which is requested to be assigned an Internet IP address by the Internet IP address assignment request s signal; address conversion table producing means which, each time the IP address assigning means assigns an Internet IP address to a mobile terminal, stores in a relational fashion the Internet IP address assigned to the mobile terminal and the mobile terminals address defined in the subnetwork in which the mobile terminal is located; and an address converter which, each time the IP address assigning means assigns an Internet IP address to a mobile terminal, sends the assigned Internet IP address to the sender of the Internet IP address assignment request signal, and which, if the data analyzing means determines that the received data is addressed to the destination designated by the Internet IP address assigned to the mobile terminal, refers to the address conversion table and converts the Internet IP address designating the destination of the data to the corresponding address defined in the subnetwork.
According to another aspect of the invention, there is provided a computer readable storage medium storing a network address conversion program executed by a computer to convert a source address or a destination address included in data transmitted between an external host server connected to the Internet and a client within a local network, the network address conversion program including: a first step in which, when an assignment request signal requesting assignment of an Internet IP address of to particular client within the local network is received from the external host server, an Internet IP address is assigned to the particular client, and the assigned Internet IP address is sent to the external host server; and a second step in which, when data addressed to the Internet IP address assigned in the first step is received from said external host server, the network address converting apparatus converts the destination of the received data to said particular client""s address defined in the local network.